Zn/H-ZS M-5轻烃芳构化催化剂中Zn与分子筛协同作用的研究

Study on synergistic action between Zn component and H-ZSM-5 in the Zn/H-ZSM-5 catalyst for aromatization of light paraffins

分析了Al2 O3 的加入引起Zn/H ZSM 5催化剂芳构化活性和选择性下降以及稳定性有所改善的原因在于高温焙烧或水热处理 ,使掺有粘结剂氧化铝的Zn/H ZSM 5催化剂表面锌组元的再分布 ,即Al2 O3 上的锌含量增加 ,而处于H ZSM 5沸石上的锌浓度降低。较为系统地探讨了Al2 O3 和ZnO/Al2 O3 的芳构化催化作用以及锌组元和ZnO/Al2 O3的引入对HZSM 5性能的影响。论证了在Zn/H ZSM 5催化剂中只有处于分子筛表面的Zn组元才能同分子筛B酸中心产生协同作用 ,从而改善H ZSM 5分子筛的芳构化活性与选择性 ,而在经过焙烧和水热处理的混有Al2 O3 的Zn/H ZSM 5催化剂中 ,分布在Al2 O3 上的锌组元几乎不与分子筛发生协同作用 。

Compared to Zn/H ZSM 5,lower aromatization activity and selectivity were obtained by the addition of Al_2O_3 to Zn/H ZSM 5 catalyst for n hexane aromatization, while the catalyst stability improved. The analytical results by TEM-EDS technique indicated that the effect of Al_2O_3 on the aromatization performance of Zn/H ZSM 5 was closely correlated with the zinc emigration from H ZSM 5 to Al_2O_3 after calcination and hydrothermal treatment. Especially, the aromatization on Al_2O_3 and Zn/Al_2O_3 and the effect of incorporation of Zn component or Zn/Al_2O_3 were studied. The experimental results showed that Al_2O_3 and Zn/Al_2O_3 had very weak aromatization activity and little effect on the catalytic properties of H ZSM 5. Therefore, it was concluded that it was only the zinc component on the surface of H ZSM 5 zeolite that could cooperate with H ZSM 5 and modify its catalytic performance, while the synergistic action couldn't take place between H ZSM 5 and zinc component on Al_2O_3.